The present invention relates to drive arrangements for continuous face underground mining. In particular, the invention relates to sprocket drives for an armoured face conveyor (AFC) rack system used with longwall shearers.
Traditional longwall shearers utilize a two-sprocket drive that moves the shearer along a mining face, and an example of such a drive is shown in U.S. Pat. No. 7,731,298. Generally, two-sprocket drive systems include a first sprocket that is driven by a drive system such as a motor. A second sprocket intermeshes with the first sprocket and further intermeshes with a rack extending along a mining face. As the driven first sprocket is rotated, the second sprocket is forced to rotate, thereby pulling the shearer along the rack. The first sprocket rotates about a first axis and the second sprocket rotates about a second axis parallel to the first axis. The second sprocket is rotatable about the first sprocket such that the vertical distance between the first axis and the second axis is adjustable. In this way, the height of the shearer may be adjusted, as desired, to accommodate various mining faces.
Traditional two-sprocket drive arrangements provide for a wide range of height adjustability. However, in low-height conditions or thin mining seams (i.e., low seams) the two-sprocket arrangement does not provide a low enough profile while also providing a desired material removal rate. Further, in a two sprocket design, wear between the top and driven sprocket can be troublesome. Since the driven sprocket must float axially with the top sprocket fixed, tooth wear can create thrust loads that can damage haulage components.